1. Field of the Invention
The present invention relates to magneto-optical head apparatuses recording/reproducing a signal to/from a magneto-optical recording medium using a laser beam and magnetic field. The present invention more particularly relates to a magneto-optical head apparatus capable of alleviating the problem of tilt when tilt is caused to the magneto-optical recording medium.
2. Description of the Background Art
A magneto-optical recording medium is known as a rewritable recording medium with a large recording capacity and high reliability, and has come into practical use as a computer memory or the like. Recently, a magneto-optical recording medium having a recording capacity of 6.0 Gbytes has been developed as an AS-MO (Advanced Storage Magneto Optical disk) standard, and will soon be come into practical use. Reproduction of a signal from such magneto-optical recording medium with high recording density is performed as follows. A magnetic domain of a recording layer of the magneto-optical recording medium is transferred to a reproduction layer, and a detection window is formed in the reproduction layer such that only the transferred magnetic domain is detected. Thus, the transferred magnetic domain is detected from the detection window. This method is called MSR Magnetically induced Super Resolution).
Another technology has also been developed in which an alternating magnetic field is applied in reproducing a signal from a magneto-optical recording medium, and a magnetic domain of a recording layer is transferred and enlarged to a reproduction layer by a laser beam and the alternating field. This is called a magnetic domain expansion readout technology. A magneto-optical recording medium capable of recording and/or reproducing a signal of 14 Gbytes has been proposed with use of this technology.
A magneto-optical head in which an evanescent light is used for recording/reproducing a signal to/from a magneto-optical recording medium with high density is disclosed in NIEKKEI ELECTRONICS ASIA, August 1997, pp.46-51. The evanescent light is produced as follows. Referring to FIG. 1A, a laser beam is collected by an objective lens 120, directed to an SIL (Solid Immersion Lens) 121 onto a point 123 at an end face of SIL 121, and then emitted from point 123. As the laser beam must be collectively directed to point 123 to produce the evanescent light, objective lens 120 and SIL 121 are integrally supported by a base 122. To direct the evanescent light to an optical disk, a distance between SIL 121 and the optical disk must not exceed 200 nm. Thus, a flying head has been proposed which allows SIL 121 to fly as the optical disk rotates at a prescribed rate.
However, use of the flying head is associated with the following problem. More specifically, if tilt is caused to the optical disk, SIL 121 also tilts with the optical disk, as shown in FIG. 1B. As a result, objective lens 120 that is supported integrally with SIL 121 also tilts. Then, an optical axis of the laser beam directed to objective lens 120 is considerably displaced from that of objective lens 120, thereby causing a focal point at point 124 rather than at proper point 123.
As described above, the use of the proposed flying head does not enable accurate recording or reproduction of the signal since the laser beam is not collected at the proper point when there is a problem of tilt.